Farmland ecosystem plays an important role in the terrestrial ecosystem carbon cycle.As the main vegetation in farmland ecosystems,crops assimilate a large amount of carbon dioxide through photosynthesis.And the carbon fixation in crops would vary with crop species,planting structure and climatic condition.Rice,corn and soybean were taken as the study objects,the carbon fixation of these crops in the main cities and counties of Sanjiang Plain were compared and analyzed for the year 1980,1985,1995,2003 and 2...